Geo Tex

I’ve been designing a calendar for 2010 featuring photographs of mountains in the Big Bend. This is the cover, Sawtooth Mountain in the Davis Mountains. I’m going to use the same photograph for the cover of Davis Mountains Vistas.

One of the photographs I’m not going to be able to use in Davis Mountains Vistas 2nd Edition is this one of the Limpia Formation, taken about 4.2 miles down Limpia Canyon from the Jeff Davis courthouse. The formation is jointed very regularly both horizontally and vertically, something often seen in thinner lava flows, but seldom as regular as here.

I am continuing to revise my book on the Davis Mountains and will include this photograph of Sleeping Lion Formation lava columns above buildings of the old fort. The formation, a gray porphyritic rhyolite, is 200 feet thick here.

The building on the far left of the photograph is one of the older officer quarters. The two double-storey buildings and the roofless building at the left are junior officer quarters built just before the fort closed in 1891. The ruin to the right is of the post chapel.

Another of my favorite mountains going down Highway 118 is Willow Mountain (3,380 feet), about 2-1/2 miles north of Study Butte, a reddish brown quartz trachyte mushroom-shaped intrusion, a trapdoor laccolith. The trapdoor opening is on the left of the photograph.

Its south face has one of the most spectacular displays of columnar jointing in the Big Bend. Jointing develops in intrusions and lava flows when they shrink as they cool. These columns are up to 400 feet long.

This photograph was taken on September 13, 2008 from the Boquillas Canyon Overlook. The river was in full flood as a result of Mexican authorities releasing water from a dam on the Rio Conchos.

I had earlier spoken to Kevin Urbanczyk of Sul Ross Geology Department at Panther Junction visitor center who was about to lead a raft trip downriver. He later told me that when they reached the La Linda bridge they had to lie flat in the raft to get under the bridge which is normally 20 feet above water level.

The more conventional view of Elephant Mountain taken from the flats along Highway 118 to the south.

Visitors to the Big Bend often ask me why Elephant Mountain (6,206 feet) is so called. It doesn’t look at all like an elephant from most angles. I think the answer is in this photograph taken about 23 miles south of Alpine in the evening sun in which the trunk is laid out along the horizon on the left and the eye is the left rock outcrop.

The outcrop is of a nepheline trachyte sill, 4 miles long, 2 miles wide and 1,200 feet thick, weighing about 3 billion tons. The rock cliffs you see towards the right of the photograph are also of the sill.

The mountain is in the 23,000-acre Elephant Mountain Wildlife Management Area. The main wildlife species are desert mule deer, pronghorn antelope, coyotes, scaled quail, rattlesnakes, whiptail lizards, spadefoot toads and bighorn sheep which were introduced in 1987. Texas Parks and Wildlife has a web page for the WMA.